Dandelion is high in calcium.
It grows in soil that is depleted in calcium and pulls it up to the surface with its deep roots, the old leaves die off and there you go, nature topdressing itself.
There’s plant species for every kind of deficiency imaginable.
I just found an interesting web page about it: What Weeds Tell You About Your Soil
Weeds are actually the plants that keep our soil healthy, they are saviors, they exist so we don’t need to think about enriching the soil. Just let everything grow, once the soil is rich again they will cease to grow. The seeds may stay in the soil, but they will only sprout when the soil is lacking in something that they are good at making available.
I see this happening with the beans in my pots, when the nitrogen levels are maxed out then the bean plants start turning black and die on their own.
Apart from that I topdress with as many different kitchenscraps, grasses, weeds, tree leaves, etc I can find nearby. I don’t have deficiencies.
When in doubt, choose everything that has lived. 
If you eat meat then throw some whole ribs in your pots, the fungi will ensure a steady supply of calcium for years to come, it will disappear eventually… nothing survives rich topsoil on a long enough timeline, only once bones sink down into clay layers is when they stay preserved, or in deserts.
But if it’s in a pot then it will be eaten by the soil biology sooner rather than later!
Dogs know this, they bury bones because it makes them softer to chew, they use the soil to help them digest it, so dogs ferment their food too.